(a) Field of the Invention
The present invention relates to a plasma display panel (PDP) unit and, more particularly, to a surface discharge type PDP having a plurality of common electrodes and a plurality of scanning electrodes on a single plane for discharging therebetween.
(b) Description of a Related Art
In general, a PDP has a large number of advantages of smaller thickness, lower flicker, larger contrast, larger display area, quicker response etc., and thus is expected for use as a flat display panel unit in a personal computer system or a workstation system as well as a wall television.
PDPs are categorized by the operational principle thereof into two types: a DC discharge type wherein uninsulated electrodes are exposed to a discharge space (or discharge gas) for operation at a DC voltage; and an AC discharge type wherein electrodes are insulated from the discharge gas by an insulating coat for operation at an AC voltage. The AC discharge type, such as used as a wall television, is further categorized by the operational principle thereof into two types: a memory type using a function of the insulator for storing electric charge in each pixel area (discharge cell); and a refreshing type which does not have a memory function. The brightness or luminance of the PDP is generally proportional to the number of repetitive discharges or the frequency of the driving pulse for the PDP. The present invention relates to any type of PDPs.
FIG. 1 shows a typical configuration of a color PDP, such as described in JP-A-8-55581. The color PDP has a front glass panel 46, a pair of optical filters 48 sandwiching therebetween the front glass panel 46 for absorbing a specified frequency range of the visible light passed by the front glass panel 46, and an electromagnetic filter 47 for absorbing electromagnetic waves radiated from the PDP as well as optical waves, which are disposed at the front side of the color PDP 45.
The described configuration is silent as to the shield for the electromagnetic waves at the rear side of the PDP 45, and thus does not have a desired electromagnetic shield function.
FIG. 2 shows a color PDP unit, such as described in JP-A-9-145918 and -9-149346. The color PDP unit includes a filter 52 including an electromagnetic shield layer at the front side of the PDP 51, wherein the filter 52 has an external terminal 52a of the electromagnetic shield layer at the rear side of the filter 52, and the external terminal 52a is in electrical contact with a metal fitting 57 used for mounting the PDP 51 at the front frame 53 of the PDP unit. A rear housing 54 of the PDP unit has a plurality of projecting bosses 58 for mounting the PDP 51 at the rear side of the PDP 51. The filter 52 is connected to the ground of the color PDP 51 through the fittings 57, the bosses 55 having a conductive coat thereon, the inner wall of the rear housing 54 and the bosses 58.
Although the described configuration has an electromagnetic shield at both the front and rear sides of the PDP 51 by enclosing the color PDP 51 with the filter 52, the front frame 53 and the rear housing 54, the color PDP unit cannot have an effective shield function if there is malfunction in electric contact between the filter 52 and the frame 53 and between the frame 53 and the housing 54. In addition, even if a sufficient electric contact is achieved between the filter 52 and the ground, a higher level of the electromagnetic radiation is not effectively shielded by the filter 52.
FIG. 3A shows another color PDP unit, such as described in JP-A-9-172267, and FIG. 3B is a sectional view taken along a plane xe2x80x9cCxe2x80x9d in FIG. 3A. The color PDP unit includes a frame body 61 made of a conductive material such as an aluminum alloy for receiving therein a color PDP 60 and a driving circuit thereof. A rear cover 63 made of plastics is fixed onto the rear side of the frame body 61 by screws 65. A front frame 62 made of plastics is also fixed onto the frame body 61 by way of screws 64. Thus, the PDP unitis shielded from electromagnetic radiation therefrom by the rear cover 63 and the front frame 62.
However, the shield function of the frame body 61, rear cover 63 and the front frame 62 is not sufficient because of the presence of the front opening of the frame body 61 and the front frame 62. Thus, the described configuration cannot provide an effective electromagnetic shield.
JP-A-9-306366 describes a color PDP unit 75 having a filter 70 shown in FIG. 4. The filter 70 is provided for shielding the electromagnetic radiation from the PDP, and includes a filter substrate 71 made of plastic resin added with pigments for selectively absorbing radiation, a reflection-resistant film 74 attached onto a side of the filter substrate 71 far from the PDP, and a silver-sputtered film 72 and an AN film 73 consecutively adhered onto the other side of the filter substrate 71 near the PDP. The silver-sputtered film 72 is made of polyethylene terephthalate (PET) sputtered by silver or inorganic substance, and the AN film 73 has a function for preventing generation of a Newton ring. The silver-sputtered film 72 is connected to the ground for discharging the voltage induced by the electromagnetic radiation.
The described configuration is also silent as to the shield from the electromagnetic radiation at the rear side of the PDP, as in the case of JP-A-8-55581 and thus does not have a sufficient electromagnetic shield function.
As described heretofore, the conventional PDP units generally use an electromagnetic shield by surrounding or enclosing the color PDP with a housing or a filter made of an electromagnetic shield substance. The techniques using the shield substance, however, generally involves higher costs because of the accuracy required in fabrication of the housing or the filter for confinement of the electromagnetic radiation within the housing or an insufficient electromagnetic shield function.
Especially, the electromagnetic shield technique using the housing or filter does not reduce the electromagnetic radiation itself. Thus, even if the electromagnetic shield is effectively performed against electromagnetic radiation from the PDP by some elements, leakage from other elements may be the next problem to be solved, iterating this procedure until a sufficient shield can be obtained as a whole. Thus, a long time and complicated fabrication process may be necessary before a sufficient shield can be obtained against the electromagnetic radiation from the PDP unit.
It is therefore an object of the present invention to provide a PDP unit having a function for reducing the electromagnetic waves without using a housing or filter made of an electromagnetic shield substance.
The present invention provides a plasma display panel (PDP) unit comprising first and second substrates opposing each other for defining therebetween a plurality of discharge cells, a plurality of first electrodes each disposed on the first substrate to extend in a row direction, a plurality of second electrodes each disposed on a first surface of the second substrate to extend in a column direction, and a first means for canceling an electromagnetic radiation from the second electrodes.
It is preferable for the first means to cancel the electromagnetic radiation from the second electrodes at least by six decibels.
In accordance with the PDP unit of the present invention, since the electromagnetic radiation from the second electrodes can be cancelled by the first means, a high-performance filter or an expensive housing is not necessary in the PDP unit, thereby reducing the costs of the PDP unit in reducing the electromagnetic radiation from the PDP unit.